1. Field of the Invention
The present invention relates to a seat mechanism for a vehicle.
2. Description of the Related Art
A seat mechanism for a vehicle which includes a slide position memory mechanism is known in the art. Such a seat mechanism has a feature which remembers an adjusted position of a front sliding seat after the front sliding seat (upper rails thereof) has been moved forward relative to lower rails. Such a feature is used when a “walk-in” operation (in which the seat back of the front sliding seat is firstly tilted forward (pivoted forward), and subsequently the front sliding seat is moved fully forward) is performed to allow passengers to enter the rear seat or to allow cargo to be stored behind the-front sliding seat.
A conventional seat mechanism for a vehicle which has such a slide position memory mechanism is disclosed in, e.g., Japanese Unexamined Patent Publication No. 8-253064. In this conventional seat mechanism, the seat back of a front sliding seat is associated with a slide lock of the front sliding seat so that the slide lock is unlocked by pivoting the seat-back forward and the slide lock is locked by returning the seat to the upright position. Due to this structure, when the front sliding seat is returned to the upright position after the completion of the walk-in operation, the slide lock is locked as soon as the seat back is returned to the upright position even before the front sliding seat reaches the position of its previous adjustment, which is remembered by the slide position memory mechanism, which may prevent full use of the slide position memory mechanism. Specifically, since it is generally the case that a front sliding seat is returned to the upright position while holding the seat back of the front sliding seat by hand after the completion of a walk-in operation, the seat back often returns to the upright position unintentionally to thereby lock the slide lock at an unintentional slide position because the seat back tends to be subject to a force in a direction to return the seat back to the upright position. This is a problem in such a type of conventional seat mechanism.
This problem can be overcome with a prior-art mechanism (disclosed in, e.g., Japanese Unexamined Patent Publication No.11-321393) which prevents the slide lock of the front sliding seat from being locked even if the seat back is returned to the upright position unless the front sliding seat is moved back to the position of its previous adjustment which is remembered by the slide position memory mechanism. However, if the seat mechanism is constructed so that the slide lock cannot be locked at all times unless the front sliding seat is moved back to the position of its previous adjustment which is remembered by the slide position memory mechanism, safety of the seat mechanism cannot be ensured when the front sliding seat cannot be moved back to the position of its previous adjustment which is remembered by the slide position memory mechanism due to a bulky luggage or the like in the rear seat. Namely, if the seat back is returned to the upright position at a position in front of the position of its previous adjustment which is remembered by the slide position memory mechanism, it is then possible for the front sliding seat to be sat in even though the slide lock thereof is not locked. In this unlocked state, if a passenger or a driver sits in the front sliding seat, there is a high possibility of the front sliding seat accidentally sliding along the lower rails, which may pose a danger to the passenger or the driver.
In the above noted conventional seat mechanism disclosed in Japanese Unexamined Patent Publication No.8-253064, the seat back of a front sliding seat is inter-geared with a slide position memory mechanism. Specifically, in this conventional seat mechanism, a shoe that is a component of the slide position memory mechanism is in a memory release position (relative to the lower rails) at which the shoe can move relative to the lower rails so that the slide position memory mechanism does not operate. On the other hand, pivoting the seat back forward causes the shoe to move to a memory position (relative to the lower rails) at which the shoe is prevented from moving relative to the lower rails. This prevents the front sliding seat from moving rearward beyond the shoe, thus bringing the slide position memory mechanism into operation. When the seat back returns to the upright position, the tension in the wire cable, which connects the seat back with a lock member pivoted to an upper rail, is loosened to thereby cause the lock member to rotate in a predetermined rotational direction by the biasing force of a spring which continuously biases the lock member in the predetermined rotational direction. This rotation of the lock member causes a catch member, by which a locking state between the shoe and the lower rail is held, to rotate by a pin-shaped second finger which projects from the lock member, thus releasing a locked state between the shoe and the lower rail. Concurrently with this lock releasing operation, a pin-shaped first finger which is fixed to the lock member is engaged with a rear end surface of the shoe, so that moving the front sliding seat (upper rails) forward causes a seat moving force thereof to be transferred to the shoe via the first finger to move the shoe forward together with the front sliding seat.
It can be understood from the above descriptions that two different operations: the lock releasing operation between the lower rail and the shoe at an operation pivoting the seat back to the upright position, and an operation transferring a moving force of the sliding seat to the shoe are performed with two pins fixed to the lock member, i.e., with the aforementioned first and second fingers, respectively. Due to this structure, the lock member is required to be made with a high working accuracy. If the first and second pins deviate from their original positions, the aforementioned two operations (the lock releasing operation and the seat-moving-force transfer operation) cannot be performed smoothly.